PIC24FJ128GA MICROCHIP [Microchip Technology], PIC24FJ128GA Datasheet - Page 164

• Manufacturer Part Number: PIC24FJ128GA
• Description: General Purpose, 16-Bit Flash Microcontrollers
• Manufacturer: MICROCHIP [Microchip Technology]

PIC24FJ128GA FAMILY
19.2
The module implements a software configurable CRC
generator. The terms of the polynomial and its length
can be programmed using the CRCXOR (X<15:1>) bits
and the CRCCON (PLEN3:PLEN0) bits, respectively.
Consider the CRC equation:
To program this polynomial into the CRC generator,
the CRC register bits should be set as shown in
Table 19-1.
FIGURE 19-1:
DS39747C-page 162
D
PLEN<3:0>
OUT
XOR
Overview
IN
p_clk
BIT 0
Hold
OUT
x
16
0
+ x
CRC SHIFTER DETAILS
12
+ x
5
X1
0
1
+ 1
IN
p_clk
Hold
BIT 1
OUT
1
Preliminary
CRC Shift Register
X2
0
1
CRC Write Bus
TABLE 19-1:
Note that for the value of X<15:1>, the 12th bit and the
5th bit are set to ‘1’, as required by the equation. The
0th bit required by the equation is always XORed. For
a 16-bit polynomial, the 16th bit is also always
assumed to be XORed; therefore, the X<15:1> bits do
not have the 0th bit or the 16th bit.
The topology of a standard CRC generator is shown in
Figure 19-2.
IN
PLEN3:PLEN0
p_clk
Hold
BIT 2
OUT
Bit Name
X<15:1>
2
CRC Read Bus
EXAMPLE CRC SETUP
X3
0
1
© 2006 Microchip Technology Inc.
X15
000100000010000
0
1
Bit Value
IN
BIT 15
1111
p_clk
Hold
OUT
15